Photonic Systems And Methods For Encoding Data In Carrier Electromagnetic Waves

ABSTRACT

Various embodiments of the present invention are related to photonic systems and methods that can be used to encode data in carrier electromagnetic waves. In one embodiment of the present invention, a photonic switch comprises: a waveguide configured to guide electromagnetic waves; a number of holes in the waveguide that prevent propagation of the electromagnetic waves beyond the holes; a reservoir located beneath the holes and filled with a liquid having the same refractive index as the photonic crystal; and a device for forcing the liquid into the holes so that the refractive index of the holes matches approximately the refractive index of the waveguide and the electromagnetic waves can propagate within the waveguide beyond the holes.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of application Ser.No. 11/648,968, filed Jan. 3, 2007, the contents of which are herebyincorporated herein in their entireties.

TECHNICAL FIELD

Embodiments of the present invention are related to photonic systems,and, in particular, to photonic systems that can be configured to encodedata in carrier electromagnetic waves.

BACKGROUND

Since the late 1970s, photonic devices have increasingly supplantedconventional electronic devices for transmitting data. Rather thanencoding data in electrical signals and transmitting the encodedelectrical signals via signal lines, the data can be encoded inelectromagnetic waves and transmitted via photonic devices, such asoptical fibers and photonic crystal waveguides. Transmitting encodedelectromagnetic waves via photonic devices have a number of advantagesover transmitting encoded electrical signals via signal lines. First,signal degradation or loss is much less for electromagnetic wavestransmitted via photonic devices than for electrical signals transmittedvia signal lines. Second, photonic devices provide a much higherbandwidth than signal lines. For example, a single Cu or Al wire canonly transmit a single electrical signal, while a single optical fibercan be configured to transmit about 100 or more electromagnetic waves.Finally, electromagnetic waves provide a much higher data transmissionrate and eliminate electromagnetic interference.

Recently, advances in materials science and semiconductor fabricationtechniques have made it possible to fabricate computational devices thatintegrate photonic devices with electronic devices, such as memory andprocessors. In particular, photonic integrated circuits (“PICs”) are thephotonic device equivalent of electronic integrated circuits. PICs canbe implemented on a small wafer of semiconductor material that forms thebase for an integrated circuit and may include a number of waveguidesfor transmitting data encoded in electromagnetic waves to a number ofintegrated photonic and electronic devices. Unlike electronic inegratedcircuits where Si is the primary material, PICs may be composed of avariety of materials. For example, PICs may be composed of a singlesemconductor, such as Si on an insulator, or binary and ternarysemiconductors, such as lnP and Al_(x)Ga_(1-x)As, where x varies from 0to 1.

In order to effectively implement PICs, a number of passive and activephotonic components are needed. Waveguides and attenuators are examplesof passive photonic components that can be fabricated using conventionalepitaxial and lithographic methods and may be used to direct thepropagation of electromagnetic waves between electronic devices.Physicists, engineers, and computer scientists have recognized a needfor active photonic components, such as modulators and switches, whichcan be implemented in PICs to encode data in, and regulate transmissionof, electromagnetic waves.

SUMMARY

Various embodiments of the present invention are related to photonicsystems and methods that can be used to encode data in electromagneticwaves. In one embodiment of the present invention, a photonic systemcomprises a first waveguide configured to transmit a number ofelectromagnetic waves. The photonic system includes a photonic crystalwith a resonant cavity and is configured to selectively and evanescentlycouple one or more of the electromagnetic waves from the first waveguideinto the resonant cavity. The photonic system also includes a secondwaveguide positioned to transmit and extract one or more electromagneticwaves from the resonant cavity via evanescent coupling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a one-dimensional photonic crystal.

FIG. 2 illustrates an example of a two-dimensional photonic crystal.

FIGS. 3A-3B are hypothetical plots of frequency versus wave vectorz-component for a first one-dimensional photonic crystal and a secondone-dimensional photonic crystal, respectively.

FIGS. 4-5 illustrate perspective views of two two-dimensional photoniccrystals.

FIGS. 6A-6B illustrate propagation of a transverse electric field andmagnetic field modes in the two-dimensional photonic crystal shown inFIG. 5.

FIG. 7 illustrates a photonic band structure of transverse electricfield and magnetic field modes propagating in the two-dimensionalphotonic crystal shown in FIG. 4.

FIG. 8 illustrates an example of a photonic crystal with two resonantcavities and a waveguide.

FIG. 9 is a hypothetical plot of frequency versus the magnitude of wavevector for the waveguide of the photonic crystal shown in FIG. 8.

FIG. 10 illustrates an isometric view of a first photonic system thatrepresents an embodiment of the present invention.

FIG. 11A illustrates a cross-sectional view of the first photonicsystem, shown in FIG. 10, with a single semiconductor transmission layerthat represents an embodiment of the present invention.

FIG. 11B illustrates a cross-sectional view of the first photonicsystem, shown in FIG. 10, with a three-layer semiconductor transmissionlayer that represents an embodiment of the present invention.

FIG. 12 illustrates three different exemplary resonant cavityconfigurations, each resonant cavity representing an embodiment of thepresent invention.

FIG. 13 shows a plot of normalized transmission versus normalizedfrequencies for electromagnetic waves evanescently transmitted betweenwaveguides in the first photonic system, shown in FIG. 10, thatrepresents an embodiment of the present invention.

FIG. 14 illustrates an exemplary use of the photonic system, shown inFIG. 10, to filter electromagnetic waves that represents an embodimentof the present invention.

FIG. 15 illustrates an isometric view of a second photonic system thatrepresents an embodiment of the present invention.

FIG. 16A illustrates a cross-sectional view of the second photonicsystem, shown in FIG. 15, with a single semiconductor transmission layerthat represents an embodiment of the present invention.

FIG. 16B illustrates a cross-sectional view of the second photonicsystem, shown in FIG. 15, with a three-layer semiconductor transmissionlayer that represents an embodiment of the present invention.

FIG. 17 shows a plot of normalized transmission versus normalizedfrequencies for electromagnetic waves evanescently transmitted betweenthe waveguides of the second photonic system, shown in FIG. 15, thatrepresents an embodiment of the present invention.

FIGS. 18A-18B illustrate schematic representations of the secondphotonic system, shown in FIG. 15, operated as an electromagnetic wavemodulator that represents an embodiment of the present invention.

FIGS. 19A-19E show plots representing three ways in which informationcan be encoded in carrier electromagnetic waves using the secondphotonic system, shown in FIG. 15, that represents an embodiment of thepresent invention.

FIG. 20 illustrates a first exemplary photonic integrated circuitincluding four second photonic systems, shown in FIG. 15, to encodeinformation that represents an embodiment of the present invention.

FIGS. 21A-21B illustrate operation of a first photonic switch thatrepresents an embodiment of the present invention.

FIGS. 22A-22B illustrate a cross-sectional view of a waveguide and areservoir of a photonic switch that represents an embodiment of thepresent invention.

FIG. 23 illustrates a second exemplary photonic integrated circuitincluding four second photonic systems, shown in FIG. 15, thatrepresents an embodiment of the present invention.

FIGS. 24A-24B illustrate operation of a photonic-crystal-based switchthat represents an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention are related to photonicsystems and methods that can be used to regulate transmission of, andencode data in, electromagnetic waves. Note that the term “photonic” asused to describe various embodiments of the present invention refers todevices that can be used to transmit either classical electromagneticwaves or quantized electromagnetic waves with wavelengths that span theelectromagnetic spectrum. In other words, the term “photonic” as used todescribe embodiments of the present invention is not limited to devicesfor transmitting quanta of electromagnetic waves called “photons.” Inorder to assist readers in understanding descriptions of variousembodiments of the present invention, an overview of photonic crystals,waveguides, and resonant cavities is provided in a first subsection.Various system and method embodiments of the present invention aredescribed in a second subsection.

An Overview of Photonic Crystals, Waveguides, and Resonant CavitiesEmbodiments of the present invention employ concepts in photoniccrystals, ridge waveguides, and other photonic devices. The textbooksFundamentals of Optical Waveguides, by Katsunari Okamoto, Elsevier Inc.2005; Optical Waveguide Theory, by Snyder and Love, Chapman and Hall,London, 1983; and Photonic Crystals, by Jean-Michel Lourtioz,Springer-Verlag, Berlin, 2005 are just of few of many references in thisfield. In this subsection, topics in photonic crystals that relate toembodiments of the present invention are described. Additional detailsregarding ridge waveguides and other photonic devices can be obtainedfrom the above-referenced textbooks, or from many other textbooks,papers, and journal articles related to this field.

Photonic crystals are photonic devices comprised of two or moredifferent materials with dielectric properties that, when combinedtogether in a regular pattern, can modify the propagationcharacteristics of electromagnetic radiation (“ER”). FIGS. 1 and 2illustrate two of many different possible patterns in which twodifferent materials with different dielectric properties can be combinedto form a photonic crystal. Photonic crystals are typically identifiedby the number of directions in which the dielectric pattern is periodic.For example, FIG. 1 illustrates an example of a one-dimensional photoniccrystal. In FIG. 1, a photonic crystal 100 is comprised of seven layersof two different dielectrics that alternate periodically in thez-direction. Unshaded layers 101-104 are comprised of a first dielectrichaving a dielectric constant ε₁, and hash-marked layers 105-107 arecomprised of a second dielectric having a different dielectric constantε₂. The layers are regularly spaced with a repeat distance called a“lattice constant,” in the case of the lattice constant shown in FIG. 1,lattice constant a. FIG. 2 illustrates an example of a two-dimensionalphotonic crystal. The two-dimensional photonic crystal 200 comprisesalternating layers of two different dielectrics, and is periodic in boththe x-direction and the y-direction with two lattice constants a and b.Unshaded regions, such as region 201, are comprised of a firstdielectric having dielectric constant ε₁, and hash-marked regions, suchas region 202, are comprised of a second dielectric having a differentdielectric constant ε₂. Photonic crystals can also be fabricated withrepeating patterns in three dimensions. Three-dimensional photoniccrystals can be fabricated using spheres, tubes, or other solid shapescomprising a first dielectric embedded in a slab comprising a seconddielectric.

ER propagating in a dielectric can be characterized by electromagneticwaves comprising oscillating, orthogonal. electric fields, Ē, andmagnetic fields, H, and a direction of propagation, k. The electric andmagnetic fields are related by Maxwell's equations:

$\begin{matrix}{{\nabla{\cdot {\overset{\_}{H}\left( {\overset{\_}{r},t} \right)}}} = 0} & {{Equation}\mspace{14mu} 1} \\{{{\nabla{\cdot {ɛ\left( \overset{\_}{r} \right)}}}{\overset{\_}{E}\left( {\overset{\_}{r},t} \right)}} = 0} & {{Equation}\mspace{14mu} 2} \\{{\nabla{\times {\overset{\_}{E}\left( {\overset{\_}{r},t} \right)}}} = \frac{\partial{\overset{\_}{H}\left( {\overset{\_}{r},t} \right)}}{\partial t}} & {{Equation}\mspace{14mu} 3} \\{{\nabla{\times {\overset{\_}{H}\left( {\overset{\_}{r},t} \right)}}} = {{ɛ\left( \overset{\_}{r} \right)}\frac{\partial{\overset{\_}{E}\left( {\overset{\_}{r},t} \right)}}{\partial t}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

where r is spatial displacement of an electromagnetic wave in thedielectric, t is time, and ε ( r) is a dielectric constant.

Because dielectrics do not generally support free charges or freecurrents, Equations 1-4 do not include a charge density term or a volumecurrent density term. Equations 3 and 4, the curl equations, are lineardifferential equations. In both equations, the left sides express thedependence of a field on the independent spatial displacement r, and theright sides express the dependence of a field on t. The only way for adifferential quantity that varies with respect to r to remain equal to aquantity that varies with respect to t, is for the differentialquantities to equal the same constant value. Both sides of Equations 3and 4 are equal to a constant, and the method of separation of variablescan be applied to obtain:

H ( r,t)= H ( r )exp(iωt)

Ē( r,t)=Ē( r )exp(iωt)

where ω is the angular frequency of an electromagnetic wave propagatingin a dielectric.

Maxwell's curl Equations 3 and 4 can be decoupled by dividing Equation 4by the dielectric constant ε( r), applying the curl operator, andsubstituting Equation 3 for the curl of the electric field to give:

Θ H ( r )=ω² H ( r )  Equation 5

where

$\Theta = {\nabla{\times \left( {\frac{1}{ɛ(r)}{\nabla \times}} \right)}}$

is a differential operator.Equation 5 is an eigenvalue equation, where the eigenvalues are ω², andthe eigenfunctions are the corresponding magnetic fields H( r). Afterthe magnetic fields H( r) are determined according to Equation 5, theelectric field Ē( r) can be obtained by substituting H( r,t) intoEquation 3 and solving for Ē( r).

For finite dimensional photonic crystals, such as the photonic crystalsshown in FIGS. 1 and 2, the eigenvalues and eigenfunctions of Equations5 are quantized to give:

Θ H _(j)( r )=ω_(j) ² H _(j)( r )

where j is a non-negative integer value called the “band index” thatlabels the harmonic modes of the magnetic field H( r) in order ofincreasing angular frequency.

The translational symmetry of the photonic crystal can be used todetermine the functional form of the magnetic fields H _(j)( r). Forexample, the functional form of the magnetic fields H _(j)( r)propagating in the photonic crystal 100 are given by the following:

H _(j,k) _(//) ,k₂( r )=exp(i k _(//)· ρ)exp(ik_(z)z)ū_(j,k) _(//),k_(z) (z)  Equation 6

where ρ is an xy-plane vector, k _(//) is an xy-plane wave vector, k_(z)is a z-direction wave vector component, and ū_(n,k) _(//),k_(z) (z) is aperiodic function in the z-direction. The exponential term exp(i k_(//)· ρ) in Equation 6 arises from the continuous translationalsymmetry of ER propagating through the dielectric layers in thexy-plane. However, the term exp(ik_(z)z)ū_(j,k) _(//) ,k_(z) (Z) inEquation 6 arises from Bloch's theorem and the discrete translationalsymmetry imposed in the z-direction by the periodicity of the dielectricconstant of the photonic crystal 100, given by:

ε( r )=ε( r+ R )

where R=al{circumflex over (z)}, a is a lattice constant determined bythe regular pattern of the dielectric layers, and l is an integer.

The magnetic fields H _(j,k) _(//) ,k_(z) ( r) are periodic for integralmultiples of 2π/a. As a result, the associated angular frequencies arealso periodic:

$\begin{matrix}{{\omega_{j}\left( k_{z} \right)} = {\omega_{j}\left( {k_{z} + \frac{m\; 2\; \pi}{a}} \right)}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

Differences in the dielectric pattern of a photonic crystal creates oneor more range of frequencies ω_(j), referred to as “photonic bandgaps,”for which ER is prevented from propagating in the photonic crystal. Thephotonic bandgap also corresponds to an electromagnetic energy range anda range of wavelengths, denoted by λ_(j), for which the differencesbetween the dielectrics prevents ER absorption and ER propagation. Thewavelength λ_(j) of ER transmitted through a photonic crystal is relatedto the angular frequency ω_(j):

$\lambda_{j} = \frac{2\; \pi \; v}{\omega_{j}}$

where v is the velocity of ER in the photonic crystal. Certain ERfrequency ranges are not transmitted through a photonic crystal becausehigh-frequency harmonic modes tend to concentrate electromagnetic energyin dielectric regions with a low dielectric constant, whilelow-frequency harmonic modes tend to concentrate electromagnetic energyin dielectric regions with a high dielectric constant. Theelectromagnetic energy, W, can be determined from the variationalprinciple as follows:

${W\left( \overset{\_}{H} \right)} = {\frac{1}{2\left( {\overset{\_}{H},\overset{\_}{H}} \right)}{\int{{\overset{\_}{r}}\frac{1}{ɛ\left( \overset{\_}{r} \right)}{{\nabla{\times {\overset{\_}{H}\left( \overset{\_}{r} \right)}}}}^{2}}}}$

where ( H, H)=∫d r H( r)* H( r), and “*” represents the complexconjugate. The electromagnetic energy is lower for harmonic modespropagating in regions with a high dielectric constant than for modespropagating in regions of a photonic crystal with a low dielectricconstant.

The size of and range of frequencies within a photonic bandgap of aone-dimensional photonic crystal depends on the relative differencebetween the dielectric constants of the dielectrics comprising aphotonic crystal. One-dimensional photonic crystals with large relativedifferences between the dielectric constants of the materials comprisingthe photonic crystal have larger photonic bandgaps at higher frequencyranges than photonic crystals with smaller relative differences betweenthe dielectric constants.

FIGS. 3A-3B are hypothetical plots of frequency ωa/2πc versus wavevector z-component, k_(z), for a first one-dimensional photonic crystaland a second one-dimensional photonic crystal, respectively. In FIGS.3A-3B, horizontal axes, such as horizontal axis 301, correspond to wavevector z-component k_(z), and vertical axes, such as vertical axis 302,correspond to the frequency. Because the frequencies ω_(j) are periodic,as described above with reference to Equation 7, frequencies ω_(j)a/2πcare plotted with respect to wave vector z-component range −π/a and π/afor angular frequency bands j equal to 1, 2, and 3. The photonicbandgaps are identified by shaded regions 303 and 304. Lines 305, 306,and 307 correspond to the first, second, and third angular frequencybands (j=1, 2, and 3). The width 310 of the photonic bandgap 303, inFIG. 3A, is smaller than the width 312 of the photonic bandgap 304, inFIG. 3B, because the relative difference between the dielectricconstants of the materials comprising the first photonic crystal issmaller than the relative difference between the dielectric constants ofmaterials comprising the second photonic crystal. Also, the photonicbandgap 303 covers a lower range of frequencies than the range offrequencies covered by photonic bandgap 304.

Two-dimensional photonic crystals can be comprised of a regular latticeof cylindrical holes fabricated in a dielectric slab. The cylindricalholes can be air holes or holes filled with a dielectric materialdifferent from the dielectric material of the photonic slab. FIG. 4illustrates a perspective view of a two-dimensional photonic crystal. InFIG. 4, a photonic crystal 400 is comprised of a dielectric slab 401with a regular lattice of embedded cylindrical holes, such as column402. The cylindrical holes extend from the top surface to the bottomsurface of the slab 401, as indicated by a cylindrical hole 403, and canbe holes filled with air or any other material having a dielectricconstant different from the dielectric constant of the slab 401.Two-dimensional photonic crystals can also be comprised of a regularlattice arrangement of cylindrical columns surrounded by a gas or aliquid. FIG. 5 illustrates a two-dimensional photonic crystal 500 havinga regular square lattice of solid cylindrical columns, such as acylindrical column 501, surrounded by fluid, such as gas or liquid, witha dielectric constant different from the cylindrical columns.

Two-dimensional photonic crystals polarize ER propagating in theperiodic plane of the photonic crystal, and the electric and magneticfields can be classified into two distinct polarizations: (1) thetransverse electric-field (“TE”) modes; and (2) the transversemagnetic-field (“TM”) modes. The TE have H( ρ) directed normal to theperiodic plane of the photonic crystal and Ē( ρ) directed in theperiodic plane of the photonic crystal, while the TM have Ē( ρ) directednormal to the periodic plane of the photonic crystal and H( ρ) directedin the periodic plane of the photonic crystal. FIGS. 6A-6B illustratepropagation of TE and TM modes in the two-dimensional photonic crystalshown in FIG. 4. The periodic plane of the photonic crystal 400 lies inthe xy-plane, the cylindrical holes are parallel to the z-direction, andER propagates through the photonic crystal 400 in the y-direction. InFIG. 6A, an oscillating curve 601 represents the H( ρ) mode directednormal to the xy-plane, and an oscillating curve 602 represents theorthogonal Ē( ρ) mode directed in the xy-plane. In FIG. 6B, anoscillating curve 603 represents the Ē( ρ) mode directed normal to thexy-plane, and an oscillating curve 604 represents the orthogonal H( ρ)mode directed in the xy-plane.

FIG. 7 illustrates a photonic band structure of TM and TE modes of an ERpropagating in the photonic crystal shown in FIG. 4. In FIG. 7, avertical axis 701 represents the angular frequency of ER propagating inthe photonic crystal 400, and a horizontal axis 702 represents the ERpropagation paths between lattice points labeled Γ, M, and K in aphotonic crystal segment 703 of the photonic crystal 400, shown in FIG.4. Solid lines, such as solid line 704, represent TM modes, and dashedlines, such as dashed line 705, represent the TE modes. A shaded region706 identifies a photonic bandgap in which neither the TE nor TM modesare permitted to propagate in the photonic crystal 400.

The width and the frequency range covered by photonic bandgaps intwo-dimensional photonic crystal slabs, such as the photonic bandgap706, depends on the periodic spacing of the cylindrical holes,represented by lattice constant a, and the relative difference betweenthe dielectric constant of the slab and the dielectric constant of thecylindrical holes. Also, the frequency range covered by photonic bandgap706 can be shifted to a higher frequency range for larger relativedifferences between the dielectric constant of the slab and thedielectric constant of the cylindrical holes, while the photonic bandgap706 can be shifted to a lower frequency range for smaller relativedifferences between the dielectric constant of the slab and thedielectric constant of the cylindrical holes.

Two-dimensional photonic crystals can be designed to reflect ER within aspecified frequency band. As a result, a two-dimensional photoniccrystal can be designed and fabricated as a frequency-band stop filterto prevent the propagation of ER having frequencies within the photonicbandgap of the photonic crystal. Generally, the size and relativespacing of cylindrical holes control which wavelengths of ER areprohibited from propagating in the two-dimensional photonic crystal.However, defects can be introduced into the lattice of cylindrical holesto produce particular localized components. In particular, a pointdefect, also referred to as a “resonant cavity,” can be fabricated toprovide a resonator that temporarily traps a narrow range of frequenciesor wavelengths of ER. A line defect, also referred to as a “waveguide,”can be fabricated to transmit ER with frequency ranges or wavelengthsthat lie within a frequency range of a photonic bandgap. As a result, athree-dimensional photonic crystal slab can be thought of astwo-dimensional crystal having a refractive index n that depends on thethickness of the slab.

FIG. 8 illustrates an example of a photonic crystal with two resonantcavities and a waveguide. A resonant cavity can be created in atwo-dimensional photonic crystal slab by omitting, increasing, ordecreasing the size of a select cylindrical hole. For example, aresonant cavity 801 is created in a photonic crystal 800 by omitting acylindrical hole, as indicated by the empty region surrounded by adashed-line circle. Resonant cavities 801 and 805 are surrounded byeffectively reflecting walls that temporarily trap ER in the frequencyrange of the photonic bandgap. Resonant cavities can channel ER within anarrow frequency band in a direction perpendicular to the plane of thephotonic crystal. For example, the resonant cavity 801 can traplocalized TM modes and TE modes within a narrow frequency band of thephotonic bandgap. Unless the photonic crystal 800 is sandwiched betweentwo reflective plates or dielectrics that create total internalreflection, the ER resonating in the resonant cavity 801 can escape inthe direction perpendicular to the periodic plane of the photoniccrystal 800. Each resonant cavity has an associated quality (“Q”) factorthat provides a measure of how many oscillations take place in a cavitybefore the ER leaks into the region surrounding the resonant cavity.

Waveguides are photonic transmission paths that can be used to direct ERwithin a particular frequency range of the photonic bandgap from a firstlocation in a photonic crystal to a second location in the photoniccrystal. Waveguides can be fabricated by changing the diameter ofcertain cylindrical holes within a column or row of cylindrical holes,or by omitting rows of cylindrical holes. For example, in the photoniccrystal 800, a dielectric waveguide 802 is created by omitting an entirerow of cylindrical holes during fabrication of the photonic crystal 800,as indicated by the empty region between dashed lines 803 and 804. Thedielectric waveguide 802 transmits ER with wavelengths λ₀ and λ₁ along asingle path. Networks of branching waveguides can be used to direct ERin numerous different pathways through the photonic crystal. Thediameter of an electromagnetic signal propagating along a waveguide canbe as small as λ/3n, where n is the refractive index of the waveguide,while a harmonic mode volume of a resonant cavity can be as small as2π/3n .

Waveguides and resonant cavities may be less than 100% effective inpreventing ER from escaping into the area immediately surrounding thewaveguides and resonant cavities. For example, ER within a frequencyrange in the photonic bandgap propagating along a waveguide also tendsto diffuse into the region surrounding the waveguide. ER entering thearea surrounding a waveguide or a resonant cavity experiences anexponential decay in amplitude, a process called “evanescence.” As aresult, a resonant cavity can be located within a short distance of awaveguide to allow certain wavelengths of ER carried by the waveguide tobe extracted by the resonant cavity. In effect, resonant cavities arefilters that can be used to extract a fraction of a certain wavelengthof ER propagating in the waveguide. Depending on a resonant cavity Qfactor, an extracted ER can remain trapped in a resonant cavity andresonate for a time before leaking into the surroundings orbackscattering into the waveguide. For example, in FIG. 8, the resonantcavity 801 is located too far from the waveguide 802 to extract a modewith particular wavelength of ER. However, the resonant cavity 805 isable to extract a fraction of ER with wavelength λ₃ propagating alongthe waveguide 802. Thus, a smaller fraction of ER with wavelength λ₃ maybe left to propagate in the waveguide 802 along with ER of wavelengthsλ₁ and λ₂.

FIG. 9 is a hypothetical plot of frequency versus the magnitude of wavevector k

for the waveguide of the photonic crystal shown in FIG. 8. In FIG. 9,shaded regions 901 and 902 represent projected first and second bandstructures of the photonic crystal 800 in the absence of the waveguide802, shown in FIG. 8. A region 903 identifies the photonic bandgapcreated by the photonic crystal 800. Line 904 identifies a band offrequencies permitted to propagate in the waveguide 802. The number offrequency bands permitted to propagate in waveguide 802 can be increasedby increasing the size of the waveguide 802. For three-dimensionalphotonic crystals, the three-dimensional lattice parameters, thedifference between dielectric constants, and the dimensions of theinclusions determine the frequency range of photonic bandgaps.Waveguides and resonant cavities can also be fabricated inthree-dimensional photonic crystals by selectively removing or changingthe dimensions of certain inclusions.

EMBODIMENTS OF THE PRESENT INVENTION

FIG. 10 illustrates an isometric view of a first photonic system 1000that represents an embodiment of the present invention. The photonicsystem 1000 includes a first ridge waveguide 1002, a photonic crystal1004, and a second ridge waveguide 1006 that have been formed in atransmission layer 1008. The transmission layer 1008 is supported by asubstrate 1010, such as SiO₂. The photonic crystal 1004 includes atriangular lattice of holes that span the height of the photoniccrystal, such as hole 1012, and also includes a resonant cavity 1014.The resonant cavity 1014 is created by selectively omitting a hole inthe lattice of holes approximately midway between the first ridgewaveguide 1002 and the second ridge waveguide 1006. The transmissionlayer 1008 can be formed using chemical vapor deposition, the lattice ofholes and ridge waveguides 1002 and 1006 can be formed using anywell-known epitaxial or lithographic technique.

The transmission layer 1008 can be composed of a single semiconductor ora plurality of layers, each layer composed of a different kind ofsemiconductor. FIG. 11A illustrates a cross-sectional view of thephotonic system 1000 with a transmission layer 1008 composed of a singlesemiconductor that represents an embodiment of the present invention.The transmission layer 1008 can be composed of a single semiconductor,such as Si, or binary, ternary, or quaternary semiconductor compounds,such as II-VI or III-V semiconductors. For example, the transmissionlayer 1008 can be composed of either ZnTe or CdSe, both II-VIsemiconductor compounds, or either GaAs or lnP, both III-V semiconductorcompounds. FIG. 11B illustrates a cross-sectional view of the photonicsystem 1000 with a transmission layer 1008 composed of threesemiconductor layers that represents an embodiment of the presentinvention. As shown in FIG. 11B, the transmission layer 1008 is composedof an intermediate semiconductor layer 1102 sandwiched between a topsemiconductor layer 1104 and a bottom semiconductor layer 1106, whichare composed of substantially identical semiconductors. For example, theintermediate semiconductor layer 1102 can be composed of GaAs and thetop and bottom semiconductor layers 1104 and 1106 can both be composedof InP.

The number of different semiconductor materials that can be selected forthe transmission layer 1008 may be based on the wavelength ofelectromagnetic waves to be transmitted within the photonic system 1000.In other words, each semiconductor material has a differentcorresponding dielectric constant e, which is associated with thetransmission of certain wavelengths of electromagnetic radiation. Forexample, a Si transmission layer 1008 has a dielectric constant ofapproximately 11.8 and can transmit electromagnetic waves with awavelength greater than approximately 1 μm, while a GaAs transmissionlayer has a dielectric constant of approximately 8.9 and can transmitelectromagnetic waves with wavelengths greater than approximately 0.35μm.

The lattice constant a and radius of the lattice holes r can be variedto create a photonic band gap that prevent electromagnetic waves over arange of frequencies from being transmitted between the first and secondwaveguides 1002 and 1006. However, the resonant cavity 1014 can beconfigured to allow electromagnetic waves over a range of frequenciesthat lie within the photonic band gap to be transmitted between thefirst and second waveguides 1002 and 1006 via evanescent coupling. Theelectromagnetic waves are confined to the area around the resonantcavity 1504.

As described above with reference to FIG. 10, the resonant cavity 1014is created by selectively omitting a hole in the lattice of holescomprising the photonic crystal 1004. However, any number of differentkinds of resonant cavity configurations can be formed in the photoniccrystal 1004 in accordance with different system embodiments of thepresent invention. FIG. 12 illustrates three different exemplaryresonant cavity configurations, each resonant cavity representing anembodiment of the present invention. As shown in FIG. 12, a firstresonant cavity 1202 comprises a single hole with a radius larger thanthe radius r of the lattice holes, a second resonant cavity 1204comprises a single hole with a radius smaller than the radius r of thelattice holes, and a third resonant cavity 1206 can be formed byomitting holes and fabricating the surrounding holes with radii smallerthan the radius r of the lattice holes. Note that for all three resonantcavities 1202, 1204, and 1206, the lattice constant a of the photoniccrystal remains unchanged.

In addition to the configuration of the resonant cavity, the type ofsemiconductor material used to form the transmission layer determinesthe range of frequencies of electromagnetic waves that may betransmitted between the first and second waveguides 1002 and 1006. FIG.13 shows a plot of normalized transmission versus normalized frequenciesfor electromagnetic waves transmitted between the first and secondwaveguides 1002 and 1006 via the resonant cavity 1014. In FIG. 13, ahorizontal axis 1302 corresponds to normalized frequencies (α/λ) ofelectromagnetic waves resonating in the resonant cavity 1014, and avertical axis 1304 corresponds to normalized transmission of theelectromagnetic waves transmitted between the first and secondwaveguides 1002 and 1006. Normalized transmission curves 1306-1308correspond to three different transmission layer 1008 semiconductormaterials with dielectric constants 10.5, 10.45, and 10.4, respectively.The curves 1306-1308 were generated using a two-dimensional finitedifference time domain (“FDTD”) numerical method for the photoniccrystal 1004 with lattice spacing and radii related by r=0.4a. The FDTDmethod is one of many well-known numerical methods used to simulatepropagation of electromagnetic waves in photonic crystals (see e.g.,Photonic Crystals, by Jean-Michel Lourtioz et al., Springer-Verlag,Berlin, 2005, pp. 78-88). The curves 1306-1308 show that the intensitiesof electromagnetic waves are diminished by approximately ½ and that thetransmission peak shifts to higher frequencies as the dielectricconstant of the transmission layer 1008 decreases. Note also that onlyelectromagnetic waves with frequencies in the frequency domain of thecurves 1306-1308 are transmitted between the first and second waveguides1002 and 1006. For example, for a transmission layer 1008 with adielectric constant of 10.4, electromagnetic waves with normalizedfrequencies in the domain from approximate 0.297 to approximately 0.298can be transmitted between the first and second waveguides 1002 and 1006via resonant cavity 1014. However, electromagnetic waves withfrequencies outside the domain of curve 1308 are not transmitted betweenthe first and second waveguides 1002 and 1006.

FIG. 14 illustrates an exemplary use of the photonic system 1000 tofilter out electromagnetic waves that represents an embodiment of thepresent invention. As shown in FIG. 14, electromagnetic waves withwavelengths λ₁, λ₂, and λ₃ propagate in the first waveguide 1002 towardthe photonic crystal 1004. The lattice constant a and the radius r ofthe holes are dimensioned so that the electromagnetic waves λ₁, λ₂, andλ₃ fall within the photonic band gap of the photonic crystal 1004.However, the resonant cavity 1004 is configured so that only theelectromagnetic wave λ₁ can resonate in the resonant cavity 1004. As aresult, the electromagnetic waves λ₂, and λ₃ are reflected by thephotonic crystal 1004, while the electromagnetic wave λ₁ is evanescentlycoupled into the resonant cavity 1004. The electromagnetic wave λ₁ isthen evanescently coupled into the second waveguide 1006.

FIG. 15 illustrates an isometric view of a photonic system 1500 thatrepresents an embodiment of the present invention. The photonic system1500 includes a number of components that are structurally similar tothe components described above with reference to the photonic system1000, shown in FIG. 10. Therefore, in the interest of brevity,structurally similar components in the photonic system 1000 and thephotonic system 1500 have been provided with the same reference numeralsand an explanation of their structure and function is not repeated. Thephotonic crystal 1502 includes a resonant cavity 1504 locatedsubstantially midway between the first and second waveguides 1002 and1006. Although, the resonant cavity 1504 is formed by omitting a holefrom the lattice of holes, the present invention is not limit to such aconfiguration. In alternate embodiments of the present invention, theresonant cavity 1504 can be configured as described above with referenceto FIG. 12. Unlike the photonic crystal 1004 described above withreference to FIGS. 10-13, the photonic crystal 1502 includes extendedregions 1506 and 1508, which can be formed from a high refractive indexmaterial. The photonic system 1500 also includes a first electricalcontact 1510, which is supported on the transmission layer 1008, and asecond electrical contact 1512, which is supported by the extendedregion 1506. The electrical contacts 1510 and 1512 are positioned onopposite sides of the photonic crystal 1500 so that voltages can beapplied across the resonant cavity 1502. The electrical contacts 1510and 1512 can be composed of Cu, Al, Au, Ag, Pt, doped semiconductormaterials, or other suitable materials.

FIGS. 16A-16B illustrate cross-sectional views of the phoionic system1500 that represent embodiment of the present invention. As shown inFIGS. 16A-16B, the transmission layer 1008 can be comprised of a singlelayer of semiconductor material or three layers of semiconductormaterial, as described above with reference to FIGS. 11A-11B. Theelectrode 1512 is positioned on the top surface of the extended region1506.

A voltage applied across the resonant cavity 1502 between the first andsecond electrical contacts 1510 and 1512 changes the dielectric constantof the resonant cavity. In other words, a voltage applied between theelectrical contacts 1510 and 1512 shifts the transmission peaks of thephotonic system 1500. FIG. 17 shows a plot of normalized transmissionversus normalized frequencies for electromagnetic waves transmitted viaevanescent coupling between the first and second waveguides 1002 and1006 through the resonant cavity 1504 that represents an embodiment ofthe present invention. In FIG. 17, a horizontal axis 1702 corresponds tonormalized frequencies (α/λ) of electromagnetic waves resonating in theresonant cavity 1504, and a vertical axis 1704 corresponds to normalizedtransmission of the electromagnetic waves transmitted between the firstand second waveguides 1002 and 1006. Normalized transmission curves1706-1708 correspond to the resonant cavity 1504 having dielectricconstant values 10.5, 10.45, and 10.4, which are created by applyingthree different voltage levels across the resonant cavity 1504. Thenormalized curves are generated using the FDTD method described abovewith reference to FIG. 13. In other words, by applying an appropriatevoltage across the resonant cavity 1504, the dielectric constant of theresonant cavity 1504 can be shifted away from transmittingelectromagnetic waves over a particular range of frequencies. Forexample, suppose that initially the dielectric constant of the resonantcavity 1504 is approximately 10.4. As a result, the curve 1708 showsthat electromagnetic waves with frequencies ranging from approximately0.297 to approximately 0.298 can be transmitted between the first andsecond waveguides 1002 and 1006. However, when an appropriate voltage isapplied between the electrical contacts 1510 and 1512, the dielectricconstant of the resonant cavity can be shifted to 10.5, whichcorresponds to the curve 1706. As shown in FIG. 17, the electromagneticwaves with frequencies ranging from approximately 0.297 to approximately0.298 can no longer be transmitted between the first and secondwaveguides 1002 and 1006.

Note that by comparing the normalized transmissions shown in FIGS. 13and 17, the high refractive index extended regions 1506 and 1508decrease the transmission of electromagnetic waves between the first andsecond waveguides 1002 and 1006. In alternate embodiments of the presentinvention, this transmission decrease can be avoided by etching air gapsbetween the second waveguide 1006 and the extended regions 1506 and1508. Otherwise, the transmission drops by approximately 4.1 dB for Δε/εequal to approximately 0.0048 and by approximately 14.0 dB for Δε/εequal to approximately 0.0095, respectively. Also note that theelectrical contacts 1510 and 1512 do not affect transmission ofelectromagnetic waves.

The photonic system 1500 can be operated as a modulator to encodeinformation in carrier electromagnetic waves (“carrier waves”). FIGS.18A-18B illustrate schematic representations of the photonic system 1500operated as a modulator that represents an embodiment of the presentinvention. In FIG. 18A, the photonic system 1500 is electronicallycoupled to a first node 1802, which can be a processor, memory, or otherdata storage or data generating electronic device. The first node 1802encodes data in electrical signals that are transmitted to the photonicsystem 1500. A source 1804 generates a carrier wave λ_(CW) that is alsotransmitted to the photonic system 1500. Now referring to FIG. 18B, thecarrier wave λ_(CW) generated by the source 1804 is transmitted in thefirst waveguide 1002 to the photonic crystal 1502. The carrier waveλ_(CW) is evanescently coupled into the resonant cavity 1504. While thecarrier wave λ_(CW) is evanescently coupled into the resonant cavity1504, the electrical contacts 1510 and 1512 also receive the electricalsignals that generate an oscillating voltage, that also encodes theinformation generated by the node 1802, across the resonant cavity 1504.The voltage oscillations modulate the carrier wave λ_(CW) to generate amodulated electromagnetic wave λ_(MOD) that encodes the same informationand is evanescently coupled into the second waveguide 1006. Returning toFIG. 18A, the modulated electromagnetic wave λ_(MOD) can be transmittedover large distances in an optical fiber 1806 to a second node 1808 forprocessing. In alternate embodiments of the present invention, themodulated electromagnetic wave λ_(MOD) can be transmitted over photoniccrystal waveguides, ridge waveguides, or through free space.

FIGS. 19A-19E provide a conceptual representation of encodinginformation in carrier waves using the photonic system 1500 as describedabove with reference to FIGS. 18A-18B that represents an embodiment ofthe present invention. Information in computational systems is typicallyrepresented by sequences of bits. Each bit is equivalent to a choicebetween two alternatives, such as “yes” and “no,” or “on” and “off.” Thetwo states for a single bit are typically represented by the binarynumbers “1” and “0.” Although an electromagnetic wave comprises amagnetic field component and an electric field component, for the sakeof simplicity, the carrier wave is represented in the followingdiscussion by the electric field component:

E(z,t)=E₀ cos(zk−ωt)

where the electric field propagates in the z direction, ω is angularfrequency, k is a wavevector ω/c, t is time, and E₀ is the electricfield amplitude. FIG. 19A shows a plot of the electric field componentof a carrier wave versus time. In FIG. 19A, and in subsequent FIGS.19C-19E, a horizontal line 1902 is a time axis and a vertical line 1904is the amplitude E. A curve 1906 represents the electric field componentE(z,t) of a carrier wave with a regular vibrational frequency. Thecarrier wave 1906 is transmitted in the first waveguide 1002 andevanescently coupled into the resonant cavity 1504. In order to producethe modulated electromagnetic wave λ_(MOD) described above withreference to FIG. 18, the voltage across the resonant cavity 1504 isvaried in accordance with the electrical signals provided by the firstnode 1802, shown in FIG. 18A. FIG. 19B shows a plot of voltage versustime of an oscillating voltage encoding a binary number “10101” thatrepresents one of many possible ways in which the voltage applied to theresonant cavity 1504 can be varied to encode information. The lowervoltages 1908-1910 correspond to the binary number “1,” while the highervoltages 1911 and 1912 correspond to the binary number “0.”

The photonic system 1500 can produce the modulated electromagnetic waveλ_(MOD) by modulating the carrier wave λ_(CW) amplitude. FIG. 19Cillustrates an example of an amplitude modulated electromagnetic waveλ_(MOD) encoding the binary sequence “10101” in accordance with thevoltage shown in FIG. 19B. In FIG. 19C, a single bit corresponds to fourconsecutive cycles of the signal. The cycles 1914 and 1915 have smallamplitudes, which correspond to the binary number “0” and are achievedby shifting the dielectric constant of the resonant cavity 1504 awayfrom transmitting the carrier wave between the first and secondwaveguides 1002 and 1006 when the voltage across the resonant cavitycorresponds to the higher voltage levels 1911 and 1912, respectively, asdescribed above with reference to FIG. 17. The cycles 1916-1918 havelarge amplitudes, which correspond to the binary number “1” and areachieved by little to no shifting of the dielectric constant of theresonant cavity 1504 when the voltage across the resonant cavity 1504corresponds to the lower voltage levels 1908-1910, respectively.

The photonic system 1500 can also produce the modulated electromagneticwave λ_(MOD) by modulating the carrier wave λ_(CW) frequency or phase.FIGS. 19D-19E represent frequency and phase modulated electromagneticwaves, respectively, and each can be accomplished by applyingappropriate oscillating voltages to change the dielectric constant ofthe resonant cavity 1504. FIG. 19D illustrates an example of a frequencymodulated electromagnetic signal encoding of the binary number “10101”in accordance with a voltage pattern not shown. In FIG. 19D, the lowerfrequency cycles 1920-1922 correspond to the binary number “1,” andhigher frequency cycles 1923 and 1924 correspond to the binary number“0.” Phase modulation is used to encode information by shifting thephase of the carrier wave as follows:

E(z,t)=E ₀ cos(zk−ωt+φ)

where φ represents a phase shift. FIG. 19E illustrates an example of aphase modulated electromagnetic wave encoding of the binary numbers “0”and “1.” In FIG. 19E, the cycles 1924-1926 correspond to a binary number“1,” and the cycles 1927 and 1928 include a ½ cycle phase shift from thecycles 1924-1926 and correspond to the binary number “0.” Theelectromagnetic signals can also be modulated for telecommunicationssignals. For example, electromagnetic signals can be modulated for areturn-to-zero (“RZ”) or non-return-to-zero (“NRZ”) line codes intelecommunication signals.

The photonic system 1500 can be used to encode information in a PIC.FIG. 20 illustrates an exemplary PIC 2000 including four photonicsystems to encode information that represents an embodiment of thepresent invention. The PIC 2000 includes a source 2002, six nodes2004-2009, four photonic systems 2010-2013, and two optical fibers 2014and 2015 that are coupled to other optical or electronic devices (notshown). The nodes 2004-2009 can be any combination of electronicprocessors, memory, sensors, or other electronic data generatingdevices. The photonic systems 2010-2013 are electronically coupled tothe nodes 2004-2007, as described above with reference to FIG. 18A. Thesource 2002 is coupled to the photonic systems via waveguides, such aswaveguide 2016. The waveguides can be ridge waveguides or photoniccrystal waveguides in a single transmission layer, or optical fibers.The source 2002 generates a carrier wave λ_(CW) that is transmitted viathe waveguides to photonic systems 2010-2013. The nodes 2004-2007 encodeinformation in the carrier wave λ_(CW) to produce four differentlymodulated electromagnetic waves λ_(MOD), as described above withreference to FIGS. 18-19. The modulated electromagnetic waves λ_(MOD)are transmitted separately to the nodes 2008 and 2009 and the opticalfibers 2014 and 2015.

A PIC may also include photonic switches at waveguide junctions forregulating transmission of carrier waves to different nodes. Forexample, as shown in FIG. 20, photonic switches may be located at ridgewaveguide junctions 2018-2020. FIGS. 21A-21B illustrate operation of afirst photonic switch 2100 that represents an embodiment of the presentinvention. The photonic switch 2100 comprises a single ridge waveguide2102 that bifurcates into a first ridge waveguide 2104 and a secondridge waveguide 2106. As shown in FIG. 21A, the first ridge waveguide2104 includes holes 2108-2110, and the second ridge waveguide 2106include holes 2111-2113. The holes 2108-2113 prevent a carrier waveλ_(CW) from being transmitted through the first and second ridgewaveguides 2104 and 2106. As a result, the first and second waveguides2104 and 2106 are said to be turned “off.” On the other hand, thecarrier wave λ_(CW) can be transmitted through either of the first andsecond waveguides 2104 and 2106 by filling the holes with a liquidhaving a refractive index that is substantially identical to therefractive index of the first and second waveguides 2104 and 2106. Asshown in FIG. 21B, three dotted circles represent the holes 2108-2110 inthe waveguide 2204 that are filled with the liquid. As a result, thecarrier wave λ_(CW) can be transmitted beyond the junction via the firstwaveguide 2104, which is said to be turned “on.”

FIGS. 22A-22B illustrate a cross-sectional view of three holes in awaveguide of a photonic switch that represents an embodiment of thepresent invention. As shown in FIG. 22A, a waveguide 2202 includes threeholes 2204-2206 that span the height of the waveguide 2202. A reservoir2208 is located within the substrate 2210 and beneath the three holes2204-2206. The reservoir 2208 is filled with a liquid havingsubstantially the same refractive index as the waveguide 2202. Thephotonic switch also includes a resistor coil 2212 connected to anelectrical source 2214. In other words, the resistor coil 2212 operatesas a heating element that heats the liquid within the reservoir 2208.

Turning the waveguide 2202 “on” and “off” is described with reference toFIGS. 22A-22B. Referring to FIG. 22A, none of the liquid stored in thereservoir 2208 fills the holes 2204-2206. As a result, the carrier waveλ_(CW) is not transmitted beyond the holes 2204-2206 and the waveguideis turned “off.” However, referring to FIG. 22B, the waveguide 2202 canbe turned “on” when an electrical current generated by the electricalsource 2214 is passed through the resistor coil 2212. The resistor coil2212 heats up, which heats the liquid in the reservoir 2208 causing theliquid to expand and fill the holes 2204-2206. Because the liquid has arefractive index that is substantially identical to the refractive indexof the waveguide 2202, the carrier wave λ_(CW) is transmitted beyond theholes 2204-2206. The waveguide 2202 is turned “off” by turning “off” theelectronic source 2214 and by allowing the liquid to cool and contract.

In an alternate embodiment of the present invention, photonic switchesmay be fabricated in a PIC using photonic crystal waveguide junctions.FIG. 23 illustrates a second exemplary PIC 2300 including photonicsystems that represents an embodiment of the present invention. The PIC2300 includes a number of components that are structurally similar tothe components described above with reference to the PIC 2000, shown inFIG. 20. Therefore, in the interest of brevity, structurally similarcomponents have been provided with the same reference numerals and anexplanation of their structure and function is not repeated. However,unlike the PIC 2000, shown in FIG. 20, photonic-crystal-based switches2302-2304 are used to regulate transmission of carrier waves to thenodes 2004-2007.

FIGS. 24A-24B illustrate operation of a photonic-crystal-based switchthat represents an embodiment of the present invention. Thephotonic-crystal-based switch 2400 comprises a single waveguide 2402that bifurcates into a first waveguide 2404 and a second waveguide 2406.As shown in FIG. 24A, the first and the second waveguides 2404 and 2406includes three holes. The holes prevent a carrier wave λ_(CW) from beingtransmitted beyond the junction and the first and second waveguides 2104and 2106 are said to be turned “off.” The carrier wave λ_(CW) can betransmitted through the first and second waveguides 2104 and 2106 byfilling the holes with a liquid having a refractive index that issubstantially identical to the refractive index of the photonic crystalslab. As shown in FIG. 24B, three dotted-line circles in the waveguide2204 represent holes that are filled with the liquid. As a result, thecarrier wave λ_(CW) can be transmitted beyond the junction and thewaveguide 2404, and the waveguide 2204 is said to be turned “on.” Theholes can be filled as described above with reference to FIGS. 22A-22B.

Although the present invention has been described in terms of particularembodiments, it is not intended that the invention be limited to theseembodiments. Modifications within the spirit of the invention will beapparent to those skilled in the art. In an alternate embodiment of thepresent invention, those skilled in the art would recognize that moreholes can added to waveguides in the photonic switches. In alternateembodiments of the present invention, the photonic switches may three ormore waveguide that are output from a single waveguide. In alternateembodiments of the present invention, the photonic crystals 1004, shownin FIG. 10, and the photonic crystal 1502, shown in FIG. 15, can bedoped with positive carriers, negative carriers, or other dopants sothat the dielectric constant of the photonic crystals 1004 and 1502 aredifferent from that of the first and second ridge waveguides 1002 and1006. In alternate embodiments of the present invention, rather thanemploying the resistor coil 2212 to generate heat that causes the liquidto fill the holes in the photonic crystal, as a described above withreference to FIG. 22, a piezoelectric pump can be used to force theliquid stored in the reservoir into the holes.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that the specificdetails are not required in order to practice the invention. Theforegoing descriptions of specific embodiments of the present inventionare presented for purposes of illustration and description. They are notintended to be exhaustive of or to limit the invention to the preciseforms disclosed. Obviously, many modifications and variations arepossible in view of the above teachings. The embodiments are shown anddescribed in order to best explain the principles of the invention andits practical applications, to thereby enable others skilled in the artto best utilize the invention and various embodiments with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the followingclaims and their equivalents:

1. A photonic switch comprising: a waveguide configured to guide electromagnetic waves; a number of holes in the waveguide that prevent propagation of the electromagnetic waves beyond the holes; a reservoir located beneath the holes and filled with a liquid having the same refractive index as the photonic crystal; and a device for forcing the liquid into the holes so that the refractive index of the holes matches approximately the refractive index of the waveguide and the electromagnetic waves can propagate within the waveguide beyond the holes.
 2. The device of claim 1 wherein the waveguide further comprise one of: a ridge waveguide; and a photonic crystal waveguide.
 3. The device of claim 1 wherein the waveguide further comprises one of: Si; a III-V semiconductor; and a II-VI semiconductor.
 4. The device of claim 1 wherein the number of holes further comprises three or more.
 5. The device of claim 1 wherein the photonic crystal-based switch further comprises a SiO₂ substrate.
 6. The device of claim 1 wherein the device for forcing the liquid into the holes further comprises one of: a heating element located within the reservoir and in contact with the liquid so that when the temperature of the heating element is increased, the liquid expands into the holes; and a piezoelectric pump that force the liquid into the holes. 